"Self-Aware" Japanese Snake Eats Poisonous Prey for Defense

When thinking about snakes, one might first imagine its life-threatening and pain-inducing bites. Known to be extremely poisonous, these animals have long been avoided by people.

But did you know that not all of them make their own toxins? Some just robs it from frogs!

Japanese tiger keelback snake (Rhabdophis tigrinus) feeds on a toxic toads diet to become toxic too. Being usually less than a metre long, they have this specialized organs called nuchal glands that enables them to store these toxins and protect themselves from predators like birds and mammals.

Since the nuchal gland area is on the back of their necks, they arch it when threatened which makes the area more likely to be bitten. When a predator bites the exposed area, glands will immediately release a fluid to its mouth or face which can be painful.

However, keelbacks from a toad-free island was found to have a different behavior when faced with such--they escape when attacked. This raises the question on whether or not they know when they have the toxins in them.

To test this, Akira Mori of Kyoto University, Japan, and Gordon Burghardt of the University of Tennessee in Knoxville raised hatchling snakes from both toad-free and toad-loaded Japanese islands. They then divided them into those that were fed toxic toads and were not. And results showed that regardless of their habitat, when fed with toads, these snakes respond to threats the same way (displaying the gland).

“So far as I know, this is the only example in terrestrial vertebrates where there is some indication that animals act as if they are aware of when they are toxic and when they are not,” says Burghardt. How they know, however, is still an open question.

And while there are other animals that acquire toxins from their diet, Burghardt says what they've eaten don't seem to change their behaviour. “Poison dart frogs in captivity are not fed the types of food that make them toxic, but their behaviour towards predators does not seem to have changed at all,” he says.

“It is remarkable that the researchers were able to demonstrate not only a difference in behaviour between these two populations, but that if you feed toads to toxin-free snakes, they are able to adjust their behaviour in a manner consistent with being chemically defended,” says Alan Savitzky of Utah State University in Logan.